Just had an idea- - - - -instead of hammering on the slide valve, how about using a big C clamp or a ball joint press to push it into the "full flow" position? With the oil pan off, that should be a good possibility, depending on the shape of the crankcase on the inside.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!